1972 Triumph Bonneville T120V Reassembly and First Start
This 1972 Triumph Bonneville T120V came into the workshop partly assembled, with several components still in boxes and the aim of getting it back together, running and road tested.
The bike was missing a headlamp and battery, while a number of smaller parts still needed fitting, wiring or checking before an attempt could be made to start it.
Sorting through the bike and parts
The first job was to check the bike over and work through the loose parts to establish what was present and what still needed to be ordered.
The wiring harness was tidied, the alternator cable was shortened to the correct length, and several unfinished jobs around the frame and rear mudguard were completed.
The rear mudguard mounting bolts were tightened, the breather was mounted, and the rubber fuel tank mounts were checked and secured. The right-hand side cover was fitted along with a new ignition switch.
The Zener diode was wired in and properly earthed to the frame.
Preparing the new Amal carburettors
Before fitting the new Amal carburettors, both were stripped and checked internally.
New Amal carburettors can occasionally contain machining debris, so the bodies and passages were inspected for swarf before installation. The jet sizes were confirmed and the float heights were set correctly.
Once the mounting parts arrived, the carburettors were fitted to the bike and the slides were synchronised.
A new throttle cable was installed, although a crack was noted in the twist grip and replacement was recommended.
Completing the electrical system
A new headlamp and battery were fitted, followed by the horn, tachometer cable, side covers and remaining wiring connections.
Initial electrical testing confirmed that the indicators, horn, tail lamp and brake light were working.
The high-beam warning lamp was not operating, which was traced to a blown bulb. This was replaced with an LED bulb, but the warning lights were still behaving inconsistently.
Further testing found a poor earth connection within the headlamp wiring. An additional earth wire was run from the headlamp shell to the main earth feed, restoring proper operation.
The high-beam warning lamp was also illuminating with the dipped beam selected, so the wiring was corrected and retested.
Fuel system and preparation for starting
The fuel tank mounts were secured, the tank was fitted, and new fuel lines were made up and installed.
Fuel was added and the carburettors were primed to check for leaks. Both remained dry.
The HT leads were fitted and the spark plug gaps were checked and corrected before attempting the first start.
No spark traced to the points
The first starting attempt produced no spark.
Power to the ignition coils tested correctly, so attention turned to the contact breaker points. One set had no gap and both sets were dirty.
The points were cleaned and adjusted, after which the Bonneville started on the first kick.
The engine settled into a good idle. There was initially a fair amount of smoke from oil that had been sitting in the bores, but this cleared as the engine ran.
Brake adjustment and first road test
The first short run revealed that both brakes were ineffective.
The front and rear brakes were adjusted before another test. The handlebars were also found to be loose at their mounts and were tightened.
On the next road test, the bike pulled noticeably to the right. The rear wheel alignment was checked and found to be incorrect, so it was adjusted and the final drive chain free play was checked at the same time.
Rear tyre rubbing on the chain guard
A further road test revealed a loud whine from the rear wheel area.
The rear tyre was rubbing against the chain guard. The bike had been fitted with a 4.10 x 18 tyre, while the factory-recommended size was 4.00 x 18. The slightly wider tyre left insufficient clearance.
The chain guard was repositioned to provide clearance and prevent further rubbing.
Final road test
After the final adjustments, the bike was road tested again.
The brakes were working properly, the indicators and lights operated correctly, and the bike accelerated cleanly. The new Amal carburettors performed well and the engine ran strongly.
There are still minor oil leaks from the gearbox and primary, but nothing considered serious at this stage.
The Bonneville arrived partly assembled and not running. It left starting easily, riding properly, and with the unfinished electrical, fuel and chassis work completed.
Work carried out
- Checked the motorcycle and loose parts
- Compiled a list of missing components
- Inspected new Amal carburettors for swarf
- Confirmed jet sizes
- Set carburettor float heights
- Installed and synchronised the carburettors
- Installed a new throttle cable
- Installed a new headlamp and battery
- Tidied and completed the wiring harness
- Shortened and connected the alternator cable
- Installed the ignition switch
- Wired and earthed the Zener diode
- Repaired the headlamp earth circuit
- Replaced the high-beam warning bulb with an LED
- Corrected the warning lamp wiring
- Installed the horn and tachometer cable
- Installed the fuel tank, side covers and seat
- Made and installed new fuel lines
- Checked the oil tank internally
- Installed the engine breather hoses
- Checked and corrected spark plug gaps
- Cleaned and adjusted the contact breaker points
- Started the engine
- Adjusted the front and rear brakes
- Tightened the handlebar mounts
- Corrected the rear wheel alignment
- Checked final drive chain free play
- Repositioned the chain guard for tyre clearance
- Completed final road testing